of growing concerns that some of the damage from repeated concussions doesn't go away, one leading boston researcher has proposed very tough guidelines for the youngest athletes. >> we believe that kids under the age of 14 should not play collision sports as they're currently being played. >> reporter: and dr. robert cantu wants other sports to change as well. he recommends no full body checking under age 14 in ice hockey, and for soccer players, not letting the younger kids head the ball. >> the young child is particularly vulnerable to brain injury. >> reporter: at the pro level, greater recognition of the long- term effect of brain trauma prompted the nfl to enact new rules on concussions that dictate when players can get back on the field. the nfl players association even formed a traumatic brain injury committee of which dr. jim ekland is part. >> no head to head contact, and a number of things to help protect the players as the game has gotten faster and more aggressive. and the athletes have gotten more powerful. >> he says making tackle football off limits at the youth or pop warn